Structure of the Oligochceta. 89 



one of the points enumerated by Claparede which has hitherto 

 held good is the absence of a vascular plexus upon the 

 nephridia of the Limicolee, and the presence of such a plexus 

 in the Temcolse. 



Mr. Benham in 1886 (" Studies in Earthworms/' Quart. 

 Journ. Micr. Sci. vol. xxvi. pp. 215, 216) still retained the 

 division, though with some other structural distinctions. 



The TerricolaB are thus distinguished : — 



(1) Nephridia present in genital segments. 



(2) Abundant vascular network on nephridia. 



(3) Almost universal presence of a gizzard (exc. Ponto- 



drilus) . 



(4) The much smaller size of ova and the compactness of 



the ovary. 



The first character could not now be made use of, since Vej- 

 dovsky (Syst. u. Morph. d. Oligochaeten, p. 150, footnote) 

 had discovered nephridia in the genital segments of the 

 sexually mature Lumbriculus. 



The last-mentioned author {loc. cit. p. 14) .dropped this 

 scheme of classification and divided the Oligochasta into a 

 series of families corresponding to the prominent generic types. 

 The last three characters, however, still remained good, until 

 in 1887 Giard found (" Sur un Nouveau Genre de Lom- 

 briciens phosphorescents et sur l'Espece Type de ce Genre 

 Photodrilus phosphoreus, Duges," Comptes Rendus, Nov. 7, 

 1887) that Photodrilus was without a gizzard ; this was ex- 

 tended by Rosa (" Sui Generi Pontodrilus, Microscolex e 

 Photodrilus,' 1 Boll. Mus. Zool. Torino, vol. iii. No. 39, 1888) 

 to Microscolex. Criodrilus also possesses no gizzard, and 

 apparently Pymceodrilus. Photodrilus and Pontodrilus also 

 render it necessary to dispense with the first of Mr. Benham's 

 characters, for in them the nephridia do not commence until 

 the 14th or 15th segment. 



Notwithstanding these facts Rosa (" Nuova Classificazione 

 dei Terricoli," Boll. Mus. Zool. Torino, vol. iii. 1888, 

 No. 41) adhered so far to the Classification of Claparede as 

 to retain his group Terricolse; he admitted, however, the un- 

 tenability of the group Limicola3. 



The latest contribution to the question is by Mr. Benham 

 (" An Attempt to classify Earthworms," Quart. Journ. Micr. 

 Sci. vol. xxxi. pp. 201 et seq.). He distinguishes two sub- 

 classes, viz. Naidomorpha and Lumbricomorpha. These are 

 distinguished mainly on account of the occurrence of asexual 

 reproduction in the former, and its absence in the latter. The 

 statement that the blood in the Naidomorpha is uncoloured is 

 only partially true, for in Naids it is yellowish red. If it be 



